vSphere Replication Guest OS Quiescing

http://serverfault.com –
I am using vSphere Replication 5.1 to send virtual machines off to a separate datastore every 24 hours. One option in configuring each VMs replication is the Guest OS Quiescing option. Options are None and MS Shadow Copy Services (VSS). I not sure what the pros and cons of this option are and can't find much information explaining it. Anyone have any experience with this?
(HowTos)